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FreeBSD-SA-01:17                                           Security Advisory
                                                                FreeBSD, Inc.

Topic:          exmh symlink vulnerability

Category:       ports
Module:         exmh2
Announced:      2001-01-29
Credits:        Stanley G. Bubrouski <stan@CCS.NEU.EDU>
Affects:        Ports collection prior to the correction date.
Corrected:      2001-01-22
Vendor status:  Updated version released
FreeBSD only:   No

I.   Background

exmh is a tcl/tk based interface to the mh mail user agent.

II.  Problem Description

The exmh2 port, versions prior to 2.3.1, contains a local
vulnerability: at startup, if exmh detects a problem in its code or
configuration an error dialog appears giving the user an option to
fill in a bug report and email it to the maintainer.  If the user
agrees to mail the maintainer a file named /tmp/exmhErrorMsg is
created.  If the file exists and is a symlink, it will follow the
link, allowing local files writable by the user to be overwritten.

The exmh2 port is not installed by default, nor is it "part of
FreeBSD" as such: it is part of the FreeBSD ports collection, which
contains over 4500 third-party applications in a ready-to-install
format.  The ports collections shipped with FreeBSD 3.5.1 and 4.2
contain this problem since it was discovered after the releases.

FreeBSD makes no claim about the security of these third-party
applications, although an effort is underway to provide a security
audit of the most security-critical ports.

III. Impact

Malicious local users may cause arbitrary files writable by the user
running exmh to be overwritten, in certain restricted situations.

If you have not chosen to install the exmh2 port/package, then your
system is not vulnerable to this problem.

IV.  Workaround

Deinstall the exmh2 port/package, if you have installed it.

V.   Solution

One of the following:

1) Upgrade your entire ports collection and rebuild the exmh2 port.

2) Deinstall the old package and install a new package dated after the
correction date, obtained from:

ftp://ftp.FreeBSD.org/pub/FreeBSD/ports/i386/packages-3-stable/mail/exmh-2.3.1.tgz
ftp://ftp.FreeBSD.org/pub/FreeBSD/ports/i386/packages-4-stable/mail/exmh-2.3.1.tgz
ftp://ftp.FreeBSD.org/pub/FreeBSD/ports/i386/packages-5-current/mail/exmh-2.3.1.tgz

[alpha]
Packages are not automatically generated for the alpha architecture at
this time due to lack of build resources.

3) download a new port skeleton for the exmh2 port from:

http://www.freebsd.org/ports/

and use it to rebuild the port.

4) Use the portcheckout utility to automate option (3) above. The
portcheckout port is available in /usr/ports/devel/portcheckout or the
package can be obtained from:

ftp://ftp.FreeBSD.org/pub/FreeBSD/ports/i386/packages-3-stable/devel/portcheckout-2.0.tgz
ftp://ftp.FreeBSD.org/pub/FreeBSD/ports/i386/packages-4-stable/devel/portcheckout-2.0.tgz
ftp://ftp.FreeBSD.org/pub/FreeBSD/ports/alpha/packages-4-stable/devel/portcheckout-2.0.tgz
ftp://ftp.FreeBSD.org/pub/FreeBSD/ports/i386/packages-5-current/devel/portcheckout-2.0.tgz
ftp://ftp.FreeBSD.org/pub/FreeBSD/ports/alpha/packages-5-current/devel/portcheckout-2.0.tgz

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